United States v. Aetna (1999) Summary: Merger of Aetna and Prudential, two of the largest insurance companies in 1999.  The competitive concerns were in overlaps between the parties' HMO and POS plans.  While the most significant overlaps were found in Texas, the DOJ was also  concerned about the combined "purchasing power" of the parties to "depress physicians' reimbursement rates."  The merger was allowed, but the DOJ required the parties to divest HMO plans in Houston and Dallas. 

United States v. UnitedHealth (2005) Summary: Merger between dominant insurers UnitedHealth and PacifiCare.  Both insurers sold HMOs and PPOs in a number of different states.  The DOJ's investigation focused on mainly Arizona and Colorado.  Merger was consummated, but the parties were forced to divest all commercial health insurance in Tucson, AZ and Boulder, CO.  United was also forced to terminate its "network access agreement with Blue Shield of California."

United States v. UnitedHealth (2008) Summary: Merger between UnitedHealth and Sierra Health.  Sierra's main focus was Medicare Advantage plans, but was also the largest insurer in the State of Nevada.  The combined United and Sierra would have had a 94% market share for Medicare Advantage enrollees in Las Vegas.  DOJ forced the parties to only divest Sierra's Medicare Advantage portfolio.

Independence Blue Cross and Highmark's failed merger (2009) Summary: The merger of Independence and Highmark would have created an entity with 73% market share in Pennsylvania. The Pennsylvania Insurance Department opposed the merger, and in 2009 the parties dropped their plans to merge.

Blue Cross Blue Shield of Michigan and Physicians Health Plan of Mid-Michigan failed merger (2010) Summary: Blue Cross had a 70% market share while PHP had a 20% market share and controlled the largest hospital system in the state of Michigan.  After the DOJ threatened to file suit to prevent the merger, the parties abandoned the transaction.

United States v. Humana (2012) Summary: Merger between Humana and Arcadian Management Services.  Both parties primary business is through Medicare Advantage plans.  The DOJ concluded that there were significant overlaps in five different states-- Arizona, Arkansas Louisiana, Oklahoma, and Texas.  The parties were allowed to merge, but they were required to divest Arcadian's Medicare Advantage plans in 51 counties throughout the five states.

United States v. WellPoint (2012) Summary: Merger between WellPoint, acquired by Anthem in 2004, and Amerigroup. Amerigroup specialized in Medicaid Managed Care products.  The DOJ allowed the parties to consummate the merger, but required Amerigroup to sell its Medicaid Managed Care plans in Northern Virginia.